Thermomechanical aging effects on vertical marginal gap and fracture resistance: a comparative study of Bioflx and traditional pediatric crowns

Abstract

Background Various types of crowns are used for full-coverage restoration of primary teeth affected by caries, developmental defects, or after pulp therapy. Prefabricated Stainless Steel and Zirconia crowns are commonly utilized. Bioflx crowns, which blend the properties of Stainless Steel and Zirconia, provide a flexible and aesthetically pleasing alternative. Aim This study aimed to evaluate the vertical marginal gap and fracture resistance of Bioflx pediatric crowns compared to Zirconia and Stainless Steel crowns following thermomechanical aging. Methods This in-vitro study was conducted using mandibular second primary crowns of three different materials (n = 30). Crowns were divided into three groups; Zirconia crowns group (n = 10, Nu Smile, USA), Bioflx crowns group (n = 10, Nu Smile, USA) and Stainless Steel crowns group (n = 10, Nu Smile, USA). The crowns were cemented onto standardized acrylic resin dies and subjected to thermomechanical aging. Vertical marginal gap measurements were obtained using a USB digital microscope with an integrated camera, while fracture resistance was assessed with a universal testing machine. Data were analyzed for outliers and tested for normality using the Shapiro-Wilk or Kolmogorov-Smirnov tests, with statistical significance set at 0.05. Results Significant differences were observed in the vertical marginal gaps among the groups after cementation and thermomechanical aging (P = 0.013 and P = 0.001, respectively). Zirconia crowns exhibited the largest average marginal gap, followed by Bioflx and Stainless Steel crowns. Stainless steel crowns demonstrated the highest fracture resistance, followed by Bioflx crowns, while Zirconia crowns showed the lowest. Conclusions Bioflx crowns exhibit the largest vertical marginal gap but show greater fracture resistance compared to Zirconia crowns, although they are still less resistant than Stainless Steel crowns after undergoing thermomechanical aging.